Antibodies which bind with antigens of human immunodeficiency virus type 1 (HIV-1), such as Lymphadenopathy Associated Virus (LAV), are disclosed. Retroviruses associated with Acquired Immune Deficiency Syndrome (AIDS) are isolated from the sera of patients afflicted with Lymphadenopathy Syndrome (LAS) or AIDS. Viral extracts, structural proteins and other fractions of the retrovirus immunologically recognize the sera of such patients.